Ellipsometry is a well known means by which to monitor material systems, (samples). In brief, a polarized beam of electromagnetic radiation of one or more wavelengths is caused to impinge upon a material system, (sample), along one or more angles of incidence and then interact with a material system, (sample). Beams of electromagnetic radiation can be considered as comprised of two orthogonal components, (ie. “P” and “S”), where “P” identifies a plane which contains both an incident beam of electromagnetic radiation, and a normal to an investigated surface of a material system, (sample), being investigated, and where “S” identifies a plane perpendicular to the “P” plane and parallel to said surface of said material system, (sample). A change in polarization state in a polarized beam of electromagnetic radiation caused by said interaction with a material system, (sample), is representative of properties of said material system, (sample). (Note Polarization State basically refers to a magnitude of a ratio of orthogonal component magnitudes in a polarized beam of electromagnetic radiation, and a phase angle therebetween.) Generally two well known angles, (PSI and DELTA), which characterize a material system, (sample), at a given Angle-of-Incidence, are determined by analysis of data which represents change in polarization state. Additional sample identifying information is often also obtained by application of ellipsometry, including layer thicknesses, (including thicknesses for multilayers), optical thicknesses, sample temperature, refractive indicies and extinction coefficients, index grading, sample composition, surface roughness, alloy and/or void fraction, parameter dispersal and spectral dependencies on wavelength, vertical and lateral inhomogenieties etc.
Continuing, Ellipsometer Systems generally include a source of a beam of electromagnetic radiation, a Polarizer means, which serves to impose a linear state of polarization on a beam of electromagnetic radiation, a Stage for supporting a material system, (sample), and an Analyzer means which serves to select a polarization state in a beam of electromagnetic radiation after it has interacted with a material system, (sample), and pass it to a Detector System for analysis therein. As well, one or more Compensator(s) can be present and serve to affect a phase angle change between orthogonal components of a polarized beam of electromagnetic radiation.
A number of types of ellipsometer systems exist, such as those which include rotating elements and those which include modulation elements. Those including rotating elements include Rotating Polarizer (RP), Rotating Analyzer (RA) and Rotating Compensator (RC). The presently disclosed invention comprises a Rotating Compensator Ellipsometer System. It is noted that Rotating Compensator Ellipsometer Systems do not demonstrate “Dead-Spots” where obtaining data is difficult. They can read PSI and DELTA of a Material System over a full Range of Degrees with the only limitation being that if PSI becomes essentially zero (0.0), one can't then determine DELTA as there is not sufficient PSI Polar Vector Length to form the angle between the PSI Vector and an “X” axis. In comparison, Rotating Analyzer and Rotating Polarizer Ellipsometers have “Dead Spots” at DELTA's near 0.0 or 180 Degrees and Modulation Element Ellipsometers also have “Dead Spots” at PSI near 45 Degrees. The utility of Rotating Compensator Ellipsometer Systems should then be apparent. Another benefit provided by fixed Polarizer (P) and Analyzer (A) positions is that polarization state sensitivity to input and output optics during data acquisition is essentially non-existent. This enables relatively easy use of optic fibers, mirrors, lenses etc. for input/output.
Continuing, it is known in the art to focus a broadband beam of electromagnetic radiation onto a small spot in ellipsometers by reflective or refractive optics. Typically, said prior art systems image a small aperture onto a spot on a sample with high demagnification, and suffer from varying degrees of optical aberrations, (eg. spherical, chromatic, astigmatism etc.). Further, surfaces of mirrors can be non-ideal as a result of non-traditional manufacturing of special optics. Further, the cost of non-spherical optics is high.
A Search for relevant patents provided expired U.S. Pat. No. 3,748,015, to Offner, which reveals that it is known that spherical optics can be fashioned to relay an objective with 1:1 magnification and with essentially no aberrations. Said expired U.S. Pat. No. 3,748,015, to Offner, describes such a relay system comprising two elements:                a) a concave spherical mirror; and        c) a convex spherical mirror;said elements being arrange such that electromagnetic radiation caused to approach the concave spherical reflects at a first location thereon is reflected to said a convex spherical mirror, from which it reflects onto a second location of said concave spherical mirror, from which it reflects as a converging beam of electromagnetic radiation if the electromagnetic radiation caused to approach the concave spherical mirror at a first location was, for instance, a point source. FIG. 1 of this disclosure demonstrates a 015 patent System.        
Patents which describe reflective optics in ellipsometer systems are U.S. Pat. Nos. 6,734,967; 5,910,842 and 5,608,526 to Piwonka-Corle et al. The 526 patent is the earliest thereof to describe use of all-reflective focusing elements in an ellipsometer. U.S. Pat. Nos. 5,859,424 and 5,917,594 to Norton, are disclosed as they describe use of an apodizing filter to decrease beam spot size on a sample, and use of a negative miniscus lens to correct for spherical abberations where a spherical mirror is present in the path of an electromagnetic beam.
An important U.S. Pat. Ser. No. 5,872,630, is that to Johs et al., from which the present application is derived as a CIP via intervening CIP applications. Said 630 patent describes:                A spectroscopic rotating compensator material system investigation system comprising a source of a polychromatic beam of electromagnetic radiation, a polarizer, a stage for supporting a material system, an analyzer, a dispersive optics and at least one detector system which contains a multiplicity of detector elements, said spectroscopic rotating compensator material system investigation system further comprising at least one compensator(s) positioned at a location selected from the group consisting of:                    before said stage for supporting a material system;            after said stage for supporting a material system; and            both before and after said stage for supporting a material system;                        such that when said spectroscopic rotating compensator material system investigation system is used to investigate a material system present on said stage for supporting a material system, said analyzer and polarizer are maintained essentially fixed in position and at least one of said at least one compensator(s) is caused to continuously rotate while a polychromatic beam of electromagnetic radiation produced by said source of a polychromatic beam of electromagnetic radiation is caused to pass through said polarizer and said compensator(s), said polychromatic beam of electromagnetic radiation being also caused to interact with said material system, pass through said analyzer and interact with said dispersive optics such that a multiplicity of essentially single wavelengths are caused to simultaneously enter a corresponding multiplicity of detector elements in said at least one detector system.        
Said 630 patent also, amongst other disclosure, describes a Mathematical Regression based Calibration procedure which makes possible the use of essentially any compensator regardless of non-achromatic characteristics.
Another patent to Johs, from which the 630 patent was Continued-in Part, is U.S. Pat. No. 5,666,201, filed Sep. 20, 1995. The focus in said 201 patent comprises a detector arrangement in which multiple orders of a dispersed beam of electromagnetic radiation are intercepted by multiple detector systems. However, Claim 8 in the 201 patent, in combination with a viewing the Drawings therein, provide conception of the Spectroscopic Rotating Compensator Ellipsometer, as Claimed in Claim 1 of the JAW 630 patent and, in fact, the the 630 patent issued in view of a Terminal Disclaimer based upon the 201 patent. A CIP of the 630 patent, is U.S. Pat. No. 6,353,477 to Johs et al. which describes prefered multiple element compensators.
Also disclosed is U.S. Pat. No. 5,706,212, Issued Jan. 6, 1998, and Filed Mar. 20, 1996 for an Infrared Ellipsometer System Regression based Calibration Procedure. Said 212 patent describes use of an Substantially Achromatic Rotating Compensator and application of Mathematical Regression in a Calibration procedure which evaluates calibration parameters in both rotating and stationary components. The 212 patent describes that 2 OMEGA and 4 OMEGA associated terms are generated by a detector of a signal which passes through a compensator caused to rotate at a rate of OMEGA. Said 630 patent was Continued-in-Part therefrom, as is the present application via an intervening patent application. It is noted that the 212 patent application was filed four months prior to the earliest priority patent application, of Aspnes et al. (ie. U.S. Pat. Nos. 6,320,657 B1, 6,134,012, 5,973,787 and 5,877,859), the later of which was Filed on Jul. 24, 1996.
Relevant patents to Aspnes et al. are U.S. Pat. Nos. 6,320,657 B1, 6,134,012, 5,973,787 and 5,877,859. These patents describe a Broadband Spectroscopic Rotating Compensator Ellipsometer System wherein the Utility is found in the use of a “substantially Non-Achromatic” compensator, (see Claim 1 in the 657 patent), and selecting a Wavelength Range and Compensator so that “an effective phase retardation value is induced covering at least from 90 degrees to 180 degrees”, (012 patent), over a range of wavelengths of at least 200-800 nm. The 787 and 859 recite that at least one wavelength in said wavelength Range has a retardation imposed of between 135 and 225 Degrees, and another wavelength in the wavelength Range has a retardation imposed which is outside that retardation Range. The Utility of the Therma-wave patents derives from the identified conditions being met so that at least one of a 2 OMEGA and a 4 OMEGA coefficient provided by a detector provides usable information at a wavelength, even when said coefficient does not provide usable information at other wavelengths. Again, the identified Aspnes et al. patents recite directly, or describe the presence of a “substantially-non-Achromatic” compensator, while, it is noted at this point, the invention disclosed in this application utilizes what are properly termed substantially-achromatic or Psuedo-Achromatic compensators. It is further noted that the U.S. Pat. No. 5,716,212 patent application, from which this Application Continues-in-Part, was filed prior to Jul. 24, 1976 filing date of the 859 Aspnes et al. priority patent application. The disclosed invention then has Priority to simultaneous use of 2 OMEGA and 4 OMEGA signals provided from a detector in a spectroscopic rotating compensator ellipsometer system which utilizes “Other-Than-Substantially Non-Achromatic” Compensators, namely “Substantially-Achromatic” or “Pseudo-Achromatic” Compensators, to characterize samples, emphasis added.
A recently published PCT application is No. WO 01/90687 A2, which is based on U.S. application Ser. No. 09/575,295 filed May 3, 2001. This Application was filed by Thermawave Inc. and specifically describes separate use of a 2ω and a 4ω term to provide insight to sample thickness and temperature.
Another, U.S. Pat. No. 4,053,232 to Dill et al. describes a Rotating-Compensator Ellipsometer System, which operates utilizes monochromatic light.
Two patents which identify systems which utilize Polychromatic light in investigation of material systems, U.S. Pat. Nos. 5,596,406 and 4,668,086 to Rosencwaig et al. and Redner, respectively, were also identified.
Also identified is a patent to Woollam et al, U.S. Pat. No. 5,373,359 as it describes a Rotating Analyzer Ellipsometer System which utilizes white light. Patents continued from the 359 Woollam et al. are, U.S. Pat. No. 5,504,582 to Johs et al. and U.S. Pat. No. 5,521,706 to Green et al. Said 582 Johs et al. and 706 Green et al. Patents describe use of polychromatic light in a Rotating Analyzer Ellipsometer System.
A U.S. Pat. No. 6,034,777 to Johs et al., describes application of ellipsometry in an evacuated chamber comprising windows.
A U.S. Pat. No. 5,929,995 to Johs, is disclosed as it describes application of ellipsometry in an evacuated chamber comprising windows.
A U.S. Pat. No. 5,329,357 to Bernoux et al., is identified as it describes the use of optical fibers as input and output means in an ellipsometer system.
A U.S. Pat. No. 5,581,350 to Chen et al., is identified as it describes the application of regression in calibration of ellipsometer systems.
Additionally, patents pertaining to optical elements, and particularly to compensators/retarders per se are:
U.S. Pat. No. 4,917,461 to Goldstein, describes an achromatic infrared retarder comprised of two identical prisms in combination with a rflective surface;
U.S. Pat. No. 4,772,104 to Buhrer which describes an achromatic optical filter comprised of two birefringent disks;
U.S. Pat. No. 4,961,634 to Chipman describes an infrared achromatic retarder comprised of CdS and CdSe plates aligned with the fast axes thereof perpendicular to one another;
U.S. Pat. No. 6,181,421 to Aspnes et al., describes a tipped Berek Plate Compensator.
U.S. Pat. No. 5,946,098 to Johs, Herzinger and Green, describes numerous optical elements. In addition U.S. Pat. Nos. 6,084,674; 6,118,537; 6,100,981; 6,141,102; 6,100,981; 5,963,325; 6,084,674 to Johs et al. and to Herzinger et al. U.S. Pat. No. 6,084,675, which applications depend from application Ser. No. 08/997,311 filed Dec. 23, 1997, now said U.S. Pat. No. 5,946,098;
Additional patents which describe Compensators are U.S. Pat. No. 548,495 to Abbe; U.S. Pat. No. 4,556,292 to Mathyssek et al.; U.S. Pat. No. 5,475,525 Tournois et al.; U.S. Pat. No. 5,016,980 Waldron; and U.S. Pat. No. 3,817,624 to Martin and U.S. Pat. No. 2,447,828 to West;
And, U.S. Pat. Nos. 4,176,951 and 4,179,217 to Robert et al., are also disclosed as they describe rotating Birefringent elements in Ellipsometers which produce 2 and 4 components.
A PCT patent application, No. WO 01/086257 is also known and is disclosed as it describes a combination of an aperture and lens to define a spot on a sample.
A U.S. Pat. No. 5,793,480 to Lacey et al., is disclosed as it describes a field stop and lens combination in an ellipsometer prior to a sample.
A U.S. Pat. No. 5,166,752 to Spanier et al., is disclosed as it describes an ellipsometer with lenses and apertures before and after a sample.
A U.S. Pat. No. 4,054,812 to Lessner et al., describes a Source of Spectroscopic electromagetnic radiation which provides heat sink and ozone containment.
A U.S. Pat. No. 4,322,165 to Ellebracht et al., is disclosed as it decribes purging in a VUV Plasma Atomic Emission Spectroscopic Instrument.
A U.S. Pat. No. 4,875,773 to Burns et al., is disclosed as it describes an Optical System for a Multidetector Array Spectrograph.
A U.S. Pat. No. 6,414,302 to Freeouf, is disclosed as it describes a High Photon Energy, (up through 10 eV), Range Reflected Light Characterization System.
A U.S. Pat. No. 5,091,320 to Aspnes et al., is disclosed as it describes application of ellipsometry with an evacuated chamber.
A U.S. Pat. No. 4,770,895 to Hartley, is disclosed as it describes application of ellipsometry with an evacuated chamber.
A Published Patent Application by McAninch, No, 2002/0149774 A1 is disclosed as it describes purging a measurement region near a substrate in a metrology tool.
A J. A. Woollam CO. Flyer titled VUV-VASE (Registered Trademark), is disclosed as it describes a monochromater based rotating analyzer ellipsomete system in a purged chamber.
A U.S. Pat. No. 6,493,097 to Ivarsson, is disclosed as it describes a Detector Array in an analytical instrument using electromagnetic radiation.
A U.S. Pat. No. 5,229,833 to Stewart, is disclosed as it describes an optical sensor comprising a CCD Array.
A U.S. Pat. No. 5,337,146 to Azzam, is disclosed as it describes a spectrophotometer comprising a linear array detector.
A U.S. Pat. No. 6,031,619 to Wilkins et al., describes an imaging spectrometer with a CCD Matrix or Row detector.
A U.S. Pat. No. 5,818,596 to Imai et al., is disclosed as it describes use of purging gas to prevent contaminants on samples, but does not disclose ellipsometry or a multiple detector element detector aray.
A Published Patent Application by McAninch, No, 2002/0149774 A1 is disclosed as it describes purging a measurement region near a substrate in a metrology tool.
A Published Patent Application by Wang et al., No. 2003/0071996 A1 is disclosed as it involves purging of the environment of one beam in a system involving two beams.
A Published Patent Application by Eckert et al., No. US 2003/0150997 A1 is disclosed as it describes use of VUV wavelengths and purging.
A recent U.S. Pat. No. 6,940,596 to Uhrich et al., describes a three element focusing lens in a spectroscopic ellipsometer, in which the lenses are two convex calcium fluoride lenses disposed on opposite sides of a fused silica lens.
Regarding Articles,
An article by Johs, titled “Regression Calibration Method For Rotating Element Ellipsometers”, which appeared in Thin Film Solids, Vol. 234 in 1993 is also identified as it predates the Chen et al. patent and describes an essentially similar approach to ellipsometer calibration.
An Article titled “A New Purged UV Spectroscopic Ellipsometer to Characterize Thin Films and Multilayers at 157 nm”, Boher et al., Proc. SPIE, Vol. 3998, (June 2000) is disclosed as it describes a UV Spectroscopic Ellipsometer in combination with Purging.
A presentation titled “Characterisation of Thin Films and Multilayers in the VUV Wavelength Range Using Spectroscopic Ellipsometry and Spectroscopic Photometry”, Boher et al., 157 nm Symposium, May 2000) is disclosed as it describes a UV Spectroscopic Ellipsometer.
A paper titled “Progress in Spectroscopic Ellipsometry: Applications from Ultraviolet to Infrared”, Hilfiker et al., J. Vac. Sci. Technol. A, (July/August 2003).
A paper titled “Atomic Scale Characterization of Semiconductors by In-Situ Real Time Spectroscopic Ellipsometry”, Boher et al., Thin Solid Films 318 (1998) is disclosed as it mentions multichannel detectors.
A paper titled “Optical Characterization in the Vacuum Ultraviolet with Variable Angle Spectroscopic Ellipsometry: 157 nm and below”, Hilfiker et al., Proc. SPIE Vol. 3998 (2000) is disclosed as it describes use of the J.A. Woollam CO. VUV-VASE which is a monochromater based purged system.
A paper titled “Feasibility and Applicability of Integrated Metrology Using Spectroscopic Ellipsometry in a Cluster Tool”, Boher et al., SPIE Vol. 4449, (2001) is disclosed as it describes a multichannel ellipsometer applied outside an environmental chamber. This application required electromagnetic radiation to pass through windows to reach a sample.
Four papers authored or co-authored by Collins, which describe use of multichannels and rotating element ellipsometers, including rotating compensator, but not in an environmental chamber are:                “Characterization of Wide Bandgap Thin Film Growth Using UV-Extended Real Time Spectroscopic Ellipsometry Applications to Cubic Boron Nitride”, Zapien et al., J. of Wide Bandgap Materials, Vol 9, No. 3 (January 2002);        “Automated Rotating Element Ellipsometers: Calibration, Operation, and Real-Time Applications”, Collins, Rev. Sci. Instrum. 61 (8) (August 1990);        “Waveform Analysis With Optical Multichannel Detectors: Applications for Rapid-Scan Spectroscopic Ellipsometers”, An et al., Rev. Sci. Instrum. 62(8), (August 1991); and        “Multichannel Ellipsometer for Real Time Spectroscopy of Thin Film Deposition for 1.5 to 6.5 eV”, Zapien et al., Rev. Sci. Instrum. Vol. 71, No. 9, (September 1991).        
A book by Azzam and Bashara titled “Ellipsometry and Polarized light” North-Holland, 1977 is disclosed and incorporated herein by reference for general theory.
As well, identified for authority regarding regression, is a book titled Numerical Recipes in “C”, 1988, Cambridge University Press.
The disclosed invention applies the system of the expired 015 patent in reflectometer, spectrophotometer, ellipsometer, polarimeter and the like systems, variously combined with spatial filters.